Stella Karavas, CEO of Voltree Power, sounded a little tired of talking about trees when I reached her last week. Seems the Canton, MA, company has been inundated by press inquiries since CNN ran a spot on its tree-powered forest fire monitors last year—a flood that started all over again after MIT’s official news site featured the company on September 23. “Normally I’d say it was a great thing, but we just can’t seem to get a lot done,” Karavas says. “CNN wants to do a follow-up, and we said no. We just can’t handle any more press right now.”
Karavas did, however, spend enough time on the phone with me to fill in the whole story on Voltree, which is funded by her other company, Canton-based MagCap Engineering, a maker of custom transformers and power supplies for radar and microwave equipment. The way some media outlets have told the story, readers might get the impression that the idea of tapping trees for power sprang from students and professors at MIT, who then secured MagCap as commercial sponsor. In fact, says Karavas, it’s the other way around.
The tale is as twisted as a path through an old-growth forest. Back in 2005, Karavas explains, MagCap was “approached by an individual to design a circuit. The power source was not disclosed. The agreement on disclosing the power source was that we had to sign an NDA, and we would be 50 percent owners of the technology, however far we decided to take it.” Karavas didn’t mention the individual’s name to me, but previous press stories and patent documents identify him as Gordon Wadle, an Illinois-based inventor.
Intrigued, the company took the offer. When Wadle then disclosed that the power source was a tree, “it didn’t get a real warm reception from the engineers,” Karavas says. “But we said, ‘Here’s an outside-the-box thinker; why not test it. We have nothing to lose.'”
So MagCap’s engineers tried sticking an aluminum electrode from one end of their circuit into various trees, and a copper electrode into the ground on the other end. Lo and behold: they found that the apparatus produced a small but measurable direct current. That was potentially intriguing, since it suggested the possibility of building small electronic devices such as temperature and humidity sensors that could be attached to trees and powered by them, rather than running on batteries, which must often be replaced.
There was just one problem: The engineers had no idea how the trees were generating a current. In fact, the first stories about Wadle’s technology, back in 2006, were full of incredulity. “I’m wildly skeptical,” Jim Manwell, director of the University of Massachusetts Amherst’s Renewable Energy Resource Laboratory, told Mass High Tech in a January 2006 article. “It strikes me as pretty questionable for a number of reasons.”
But Karavas thought it was real enough to keep going. “I thought the only way to figure this out would be to sponsor some more research,” she says. Pretty soon Karavas ran into Andreas Mershin, a postdoctoral researcher at MIT’s Center for Biomedical Engineering, at a networking event. Mershin told her about a project at the center to build a photosynthetic solar cell from spinach chloroplasts. “He said they were getting power from spinach, and I told him I was getting power from trees,” says Karavas. “And he said, ‘Why don’t we do a demo.'”
Mershin was able to replicate MagCap’s results—but he still didn’t know why or how. “That’s when he said, ‘Let’s do an Undergraduate Research Opportunities Program [UROP] project on this,’ and we said, ‘Find a person and we’ll sponsor them,'” says Karavas. MagCap and Mershin chose an undergrad named Christopher Love, and put up $10,000 to cover his stipend.
Starting in the summer of 2006, Love began laboratory testing of small trees like potted Ficus plants, trying to figure out through a process of elimination where the voltage difference between trees and soil, consistently measured at 50 to 200 millivolts, was coming from. Was it a redox reaction involving dissimilar metals, like the reaction that occurs with a Galvanic “potato battery” or “lemon battery”? Was the flow of ion-charged sap creating the potential difference? Or was MagCap’s apparatus simply picking up extraneous electromagnetic fields?
Love used identical platinum electrodes to test the redox-reaction theory. He interrupted sap flow by placing razor blades in the wood above and below the tree electrode. He put the Ficus plants inside a Faraday cage to block out electromagnetic fields. But in the end—as Love, Mershin, and collaborator Shuguang Zhang finally reported in an August 2008 article in PLoS ONE, a peer-reviewed online journal published by the non-profit Public Library of Science—it became clear that
